Rotors for gas turbines usually comprise a plurality of disks which are either joined together by means of bolted connections or are welded together. In order to avoid overheating during operation and consequently to avoid reduction of the service life of the rotors which is brought about, the rotors are actively cooled. In this case, there is a difference between cooling methods for rotors which are connected by bolts and for welded rotors. The cooling methods for bolted rotors can be used in the case of welded rotors only to a limited extent because the rotor disks in the case of welded rotors are more solid in comparison to bolted rotors and internal cooling via holes would be more difficult to realize.
For welded rotors, various cooling devices with cooling passages and cooling chambers inside and outside the rotor are known.
For example, EP984138 discloses a rotor for a gas turbine, especially for a compressor, the surface of which is impinged upon by cooling streams. The cooling streams are guided via air passages through the stator blades and through openings in their blade tips directly to the rotor surface.
EP844367 discloses a welded rotor for a turbomachine with a plurality of rotor disks which have an annular cavity in each case between weld seams for the purpose of throughflow of cooling steam. The cooling medium is guided through the rotor itself radially outward to the blade roots.
EP1705339 discloses a rotor for a gas turbine with radially extending cooling air passages, these having an elliptical cross section.
In the case of rotors for gas turbines, especially the last rotor disks in the compressor, in the flow direction of the air to be compressed, are subjected to high operating temperatures on account of the compression of air. The temperature steadily increases the temperature over the length of the compressor in the process, the heat penetrating radially into the rotor. In the last rotor disks which are referred to active cooling is necessary in order to keep the material temperature below a certain level and to achieve a correspondingly anticipated service life of the rotor.
A known technique for cooling the last rotor disk of a compressor is shown in FIG. 1.
A rotor 1 for a gas turbine with a rotor axis 2 has a plurality of rotor disks 3, 4 and 5 which are interconnected by means of weld seams 6 between internal cavities H and H′—which are formed as a result of the axial joining together of the disks—and the rotor surface. The last rotor disk 3, moreover, has a recess 7 on its surface. Cooling air from outside the rotor is fed to this recess. Heat from the middle region of the last disk 3 of the compressor rotor is extracted in the direction of the arrow 8 and finally via the cooling recess. The heat discharge 8 is consequently beneficial in this case if the rotor disk is solidly designed in the axial direction. Limits are set upon a solid design in the axial direction, however, on account of the manufacturing engineering of such rotors and also on account of the necessity of being able to test these during the forging process.
EP19316115 discloses a rotor, comprising welded disks, for a steam turbine. The rotor disks have in each case recesses which extend radially outward from their center on the rotor axis so that after the welding together of the disks a cavity is formed on and around the rotor axis. The rotor is cooled on the rotor surface by means of a supplied steam flow.